Motion sensors are often utilized to detect motion of an object in relation to a surface. For example a speedometer in a vehicle is a type of motion sensor which detects the speed of motion along a road surface responsive to the rotation of a wheel of the vehicle. Motion sensors are also often used in motor control to detect and control the angular momentum thereof.
Another use of a motion sensor is illustrated herein in relation to the no!no! electric shaver available from Radiancy, Inc. of Orangeburg, N.Y., variously described in U.S. Pat. Nos. 6,825,445; 7,170,034; 7,202,446; 8,319,152; 8,367,974 and 8,389,906 the entire contents of each of which are incorporated herein by reference. In particular, in order to avoid skin burn, control of a shaving head comprising a heated element is performed responsive to detected motion.
FIG. 1A illustrates a high level schematic of an embodiment of an electric shaver 10 comprising: a case 20; a first roller 30 having a groove 35 disposed about the circumference thereof; an electric generator 40; a belt 50; a controller 60; a heated element 70; and a second roller 80 which can simply be a wheel or other fixed support instead (not shown). Case 20 secures first roller 30 and second roller 80 so as to provide smooth gliding motion for case 20 when juxtaposed with a skin surface 90, allowing for smooth motion along the skin in either of 2 opposing directions as shown by the arrows. In some embodiments, gliding in only one direction is allowed so as to ensure proper treatment.
Electric generator 40 is coupled to an input of controller 60 and heated element 70 is coupled to an output of controller 60. Belt 50 is arranged to sit within groove 35 and translate angular momentum of first roller 30, experienced by groove 35 to electric generator 40. Controller 60 thus receives an electric signal from electric generator 40 whose amplitude and sign are responsive to the speed and direction of motion of case 20 along skin surface 90. Controller 60 is arranged to control heated element 70 responsive the detected motion, and in particular to provide power to heated element 70 responsive to the detected motion of first roller 30. Optionally (not shown) the location of heated element 70 is further adjusted responsive to controller 60, typically by setting the distance between heated element 70 and skin surface 90 to a shaving position responsive to a detected motion in a predetermined travel direction in excess of a predetermined minimum, and setting the distance between heated element 70 and skin surface 90 to a stand-off position in the absence of such a detected motion. Second roller 80 provides a second rolling support for case 20 against skin surface 90.
The use of belt 50 to translate the motion of first roller 30 to electric generator 50 is however cumbersome and leads to failure due to the tendency of shaved hairs from skin surface 90 to clog the smooth motion thereof. Integrating electric generator 50 within first roller 30 is costly, since it requires electrical connections to a rotating body.
FIG. 1B illustrates a high level schematic of an embodiment of an electric shaver 100 which is in all respects similar to electric shaver 10 of FIG. 1A with the exception that a plurality of heated elements 70 are provided, and electric shaver 100 additionally exhibits a supply tether 110. Supply tether 110 may provide electric mains based power, a DC power and/or a coolant fluid for electric shaver 100 without exceeding the scope.
U.S. Published Patent Application S/N 2003/0128026 to Lutz, the entire contents of which is incorporated herein by reference, is addressed to device for sensing rotor position and detecting rotational speed over a broad range of speeds in an electric motor comprising a sense ring magnet and two analog Hall effect sensors. The requirement for a sense ring magnet adds to cost, may limit resolution and also may be a driver of minimal size limitations.
World Intellectual Property Organization International Publication WO 2004/008075 A2 to The Timken Company, the entire contents of which is incorporated herein by reference, is addressed to an apparatus and method for sensing absolute angular position. One or more linear position sensor are placed near a degrading surface of a shaft or other rotating component. The rotation of the shaft varies the air gap between the sensor and the degrading surface thereby generating signal that can be processed to determine various operating parameters of the rotating component. The requirement for a degrading surface, and the material requirements to ensure a proper output of the linear position sensor, add complexity to the mechanical design, and requires careful control of the relative position of the linear position sensor and the degrading surface, which adds to cost.
It would be desirable to provide a motion sensor arranged to detect rotational motion, preferably suitable for use with an electric shaver or other aesthetical/medical treatment apparatus, at a reduced cost.